Actually, Bay Trail will be using a GMA based on the Ivy Bridge HD4000... not all the specs are known, like how fast it will be clocked, but it will be scaled back from the 16 execution units that the HD 4000 has to just 4 but it's suppose to still deliver around 3x the performance of the present Clover Trail GMA, which uses a SGX545 at 533MHz.
If true then performance would basically catch the ATOM GMA up to the performance range of AMD's original Brazos/Fusion series.
Since the present Clover Trail GMA is already nearly 3x better than the old Pine Trail ATOM GMA 3150, which AMD Brazos/Fusion offered 5x to 9x better graphical performance... So another 3x boost should put the ATOM GMA up to that level... you still won't be able to play any high end modern games but older games like WoW, Starcraft 2, etc should finally be playable... and full HD resolution screens should be no problem as it will definitely support up to 2560x1600 resolution.
They're also reportedly pushing some other Intel features like QuickSync, so with the right apps you could possibly do some video editing that won't take forever to do.
What may be more important though is the fact Intel supports Linux drivers for their own GMA and driver support for the HD 4000 has improves since it was first released and that should translate over for the Bay Trail GMA for a better launch driver performance and reliability...
Along with 64bit support should make a lot more options available to Bay Trail than is available to the present Clover Trail.
Anandtech did a analysis on what's known so far about Bay Trail and noted that part of the architectural improvements being reported that Bay Trail should be able to prioritize resources between CPU and GPU and the GPU can be prioritized as needed to help max out performance.
Along with a more basic version of Intel's Turbo Boost technology, something akin to how it worked for Sandy Bridge, and is called Burst Mode for Bay Trail...
All the while Bay Trail is also suppose to improve power efficiency... though that remains to be seen but Clover Trail already manages to beat Cortex A9 ARM SoCs like Tegra 3 for power efficiency. So battery life should be good despite the performance increase...